1. Field of the Invention
The present invention is directed to lasers, and more particularly to an injection seeded, q-switched fiber ring laser.
2. Background Art
Fiber lasers are particularly attractive for optical remote sensing (or LIDAR) due to a number of key advantages over more traditional lasers for this application. Superior beam quality from a single mode fiber, minimal beam jitter, high efficiency, high brightness, passive cooling, and compactness make them attractive for both terrestrial and space applications. Furthermore, fiber lasers provide the required tunability and the potential of very narrow linewidth in the master oscillator-power amplifier (MOPA) configuration for spectroscopic applications such as differential absorption LIDAR (DIAL) or resonance scattering.
When operated in pulsed mode, MOPA fiber lasers suffer from amplified spontaneous emission (ASE) that degrades overall laser performance. Saturating the power amplifier (PA) with the master oscillator (MO) avoids this problem by depleting the upper state. Otherwise, fluorescence will drain energy into ASE, depleting signal gain. Depending on the rare-earth dopant, glass composition, and fiber geometry, required MO power ranges anywhere from a few hundred μW to several tens of mW, average power, while all of this power must be in the pulses. Microchip lasers are a good MO solution and very high PA peak powers have been achieved using them. However, they are not broadly tunable making them unsuitable for a number of key LIDAR applications.
Fiber ring lasers are a particularly attractive way to achieve high average power because they can be constructed with broad tunability in narrow linewidth. Furthermore, they can be Q-switched with a number of techniques to provide high peak powers and low noise.